/Engine/Source/Runtime/RenderCore/Public/ShaderMaterial.h
These are also the platform defines.
struct FShaderCompilerDefines
bool
COMPILER_GLSL
bool
COMPILER_GLSL_ES3_1
bool
COMPILER_GLSL_ES3_1_EXT
bool
ES3_1_PROFILE
bool
ESDEFERRED_PROFILE
bool
GL4_PROFILE
bool
MAC
bool
METAL_PROFILE
bool
PLATFORM_SUPPORTS_DEVELOPMENT_SHADERS
bool
VULKAN_PROFILE